This invention relates to improving coolant gas flow distribution in the gap region of a gas cooled dynamoelectric machine and, more particularly, to a baffle for improving coolant gas flow to stator ventilating ducts disposed in gas flow communication with the gap region downstream the baffle.
Although this invention may be especially applicable to hydrogen cooled dynamoelectric machines, such as large turbine generators which may have ratings of 300 KW or more, since these machines typically produce more heat that must be dissipated than lower rated machines, it is generally applicable to any gas cooled machine, such as one which uses air for coolant gas. Throughout this specification and claims appended hereto, words of physical relationship such as radial, axial, tangential, circumferential, etc., and their derivatives, are to be taken with respect to the axis of rotation of the rotor of the machine, unless otherwise noted.
A typical gas cooled dynamoelectric machine includes a rotatably mounted rotor having a stator spaced from and circumferentially surrounding the rotor. The space between the rotor and the stator of the machine is referred to generally as the gap region. The stator includes a plurality of axially stacked metal laminations separated at predetermined intervals by respective circumferentially extending stator core ventilating ducts in gas flow communication with the gap region. Toward axial ends of the machine, a fan, or other gas impelling device, is connected to the rotor to force coolant gas from the end space region of the machine into the gap region while the rotor is rotating, ultimately to flow through stator core ventilating ducts.
There may be a limited flow of coolant gas available, and thus it is desirable to limit flow of coolant gas into the gap region so that sufficient coolant gas is available for other coolant paths in the generator, while ensuring an adequate amount of coolant gas for each stator core ventilating duct. A known baffle configuration exhibits a solid profile to the flow of coolant gas and is connected to an axial end of the stator. The solid baffle radially extends into the gap region and is spaced from and circumferentially surrounds the rotor. The circumferential flow area for coolant gas between the rotor and the radially inner margin of the baffle is reduced relative to the unbaffled air gap region. An additional circumferential flow area around the solid baffle may be provided between the stator and the radially outer margin of the solid baffle.
When radially inner and outer circumferential flow areas around the solid baffle are provided, axially flowing coolant gas, being urged by the fan, strikes the solid baffle and divides into a first and second portion. The first and second portion respectively flow through the radially inner and outer circumferential flow area around the solid baffle and ultimately recombine in the gap region on the downstream side of the solid baffle.
Immediately axially downstream the solid baffle, coolant gas flow is at relatively high velocity, causing a localized reduction, or vena contracta, in static pressure of coolant gas in the gap region. Further axially downstream the solid baffle, at an axial distance from the solid baffle which depends in part on the respective velocities of the first and second flow portions of coolant gas around the solid baffle and on the radial aspect ratio of the solid baffle to coolant flow, coolant flow within the gap region becomes diffused, with a resulting increase in static pressure in the gap region. It is static pressure, or more precisely the difference in static pressure between the gap region and the housing region circumferentially surrounding the radially outer periphery of the stator, that is the principle factor causing coolant gas to flow from the gap region to the housing region through stator core ventilating ducts.
Due to relatively high velocity flow of coolant gas downstream the solid baffle and corresponding reduction in static pressure of coolant gas in the gap region, it is believed that some stator core ventilating ducts, especially stator core ventilating ducts immediately downstream the solid baffle, are being starved of, or have inadequate flow of, coolant gas. It is further believed that lack of adequate coolant gas flow in stator core ventilating ducts causes groups of the plurality of stator laminations, which define ventilating ducts having inadequate coolant gas flow, to become overheated, resulting in inefficient machine operation and limiting the maximum power output deliverable by the generator.
In addition, at axial ends of the stator, where the gap region communicates with the generator end spaces, there is a tendency for coolant gas flow to bypass several stator ventilation ducts and thus not be as effective for purposes of cooling. This bypass is due to the relatively high axial component of coolant gas flow resulting from the axial discharge of coolant gas from the generator fan, through the restricted flow areas around the solid baffle at the entrance to gap region. High axial flow velocity in the gap region produces a "venturi effect", or region of low static pressure, at entrances to stator ventilation ducts disposed at the radially inner portion of the stator core in the stator end section.
The groups of laminations defining stator ventilating ducts in the end core region of the stator are exposed to the most severe temperature environment within the machine due to heat build up caused by magnetic flux coupling from the rotor in two directions, radially and axially, the axial portion due to stray or leakage magnetic flux in the generator end turn region. Cooling of the stator end core region thus merits special attention to ensure that adequate coolant gas flow is provided to the end core region and to ventilation ducts disposed therein.
It is thus desirable to provide a method and means for raising the localized static pressure of coolant flow within the gap region so as to more effectively motivate coolant gas flow through stator ventilation ducts, especially those ducts disposed in the end core region of the stator.
Fixtures of various configurations have been described for use in the gap region of a gas cooled dynamoelectric machine for controlling the flow of coolant gas. These fixtures usually require bolting and/or tying, such as to a slot wedge, for mechanical support. The fixtures and support means may be costly, labor intensive and involve many parts, and further, may require removal of the rotor from the machine in order to install them. It might also be possible to achieve coolant flow control by attaching a flow directing device, such as a partition, on the rotor. However, embodiments using devices attached to the rotor require rotation of the device along with ability to withstand stresses caused by the rotation. Further, such rotating devices may require labor intensive installation, such as removal of the rotor.
A baffle for a dynamoelectric machine is described and claimed in U.S. Pat. No. 3,413,499--Barton, which is assigned to the assignee of the present application. The baffle of the Barton patent includes a first portion affixed to and extending radially inward from the stator end block, a second portion affixed to the first portion and axially extending along the gap region past several stator outlet passages, and a third portion affixed to the second portion and extending radially outward toward the stator. Thus, the baffle of the Barton patent essentially creates a plenum chamber which is isolated from the gap region. The plenum chamber has an input in gas flow communication with the generator end space region and outputs in gas flow communication with inputs to stator outlet ducts which it surrounds. The cantilever type configuration of the baffle of the Barton patent (i.e. non-mechanical fixed support of the axially inward end of the second and of the third portion of the baffle) may not be desirable, due to potential excessive response to vibration, and further due to coolant flow leakage between the third portion of the baffle and the stator, which would result in a lower pressure within the plenum chamber and ultimately less coolant gas flow through the endmost stator cooling passages.
Other baffle configurations for the gap region of a gas cooled dynamoelectric machine are described in U.S. Pat. Nos. 4,051,400--Armor et al and 4,264,834--Armor et al, both assigned to the assignee of the present application. The baffle of the Armor et al ('400) patent is for a reverse flow cooled dynamoelectric machine, (i.e. coolant gas flow is from gap region into end space region of machine) wherein even if it were to be used in the forward flow configuration, it would not resolve the problems of the aforementioned solid baffle, such as excessive vena contracta within the gap region. The baffle of the Armor et al ('834) patent is used to divide the air gap region into a predetermined number of zones, and to prevent coolant gas flow leakage between the resulting zones, by providing a radial blockage or seal across the axial coolant gas flow path.
Accordingly, it is an object of the present invention to provide a method and apparatus for ensuring adequate coolant gas flow through stator ventilating ducts of a gas cooled dynamoelectric machine, particularly through those ducts disposed in the stator end core region.
Another object is to provide a method and apparatus for controlling the quantity of coolant gas flow entering the gap region of a gas cooled dynamoelectric machine without need to remove the rotor.
Still another object is to provide apparatus for directing flow of coolant gas in the gap region of a gas cooled dynamoelectric machine which is easily installed and does not require many parts.
Yet another object is to provide a method and apparatus for obtaining faster static pressure recovery for coolant gas flow in the gap region than is possible using known baffle configurations.